Image Transmission System for Two-Way Television* 



By HERBERT E. IVES, FRANK GRAY and M. W. BALDWIN 



A two-way television system, in combination with a telephone circuit, 

 has been developed and demonstrated. With this system two people can 

 both see and talk to each other. It consists in principle of two television 

 systems of the sort described before the June, 1927, Convention of the 

 American Institute of Electrical Engineers. Scanning is by the beam 

 method, using discs containing 72 holes, in place of 50 as heretofore. 

 Blue light, to which the photoelectric cells are quite sensitive, is used for 

 scanning, with a resultant minimizing of glare to the eyes. Water-cooled 

 neon lamps are employed to give an image bright enough to be seen without 

 interference from the scanning beam. A frequency band of 40,000 cycles 

 width is required for each of the two television circuits. Synchronization is 

 effected by transmission of a 1275 cycle alternating current controlling 

 special synchronous motors rotating 18 times per second. Speech trans- 

 mission is by microphone and loud speaker concealed in the television 

 booth so that no telephone instrument interferes with the view of the face. 



DITRING the past few years, since the physical possibihty of 

 television has been established, the chief problems which have 

 received attention have been those of one-way transmission. In 

 particular, the experimental work in radio television has had for its 

 principal goal the broadcasting of television images, which is inher- 

 ently transmission in one direction. At the time of the initial de- 

 monstration of television at Bell Telephone Laboratories in 1927,^ 

 one part of the demonstration consisted of the transmission to New 

 York of the image of a speaker in Washington simultaneously with 

 the carrying on of a two-way telephone conversation. At that 

 time it was stated that two-way television as a complete adjunct to 

 a two-way telephone conversation was a later possibility. It is the 

 purpose of this paper to describe a two-way television system now 

 set up and in operation between the main offices of the American 

 Telephone and Telegraph Company at 195 Broadway and the Bell 

 Telephone Laboratories at 463 West Street, New York. It con- 

 sists in principle of two complete television transmitting and re- 

 ceiving sets of the sort used in the 1927 one-way television demonstra- 

 tion. In realizing this duplication of apparatus, however, a number 

 of characteristic special problems arise, and the paper deals chiefly 

 with matters peculiar to two-way as contrasted with one-way tele- 

 vision. 



* Presented at June, 1930, meeting of A.I.E.E., Toronto, Canada. 

 ' Bell System Technical Joitnial, October, 1927, ]>]>. 551-652. 



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